list_orthants should return an iterator

[lucaferranti]

Feature description

The function list_orthants at the moment returns a vector of vectors and hence allocates and it's not very efficient. It should return an iterator, similar to what DiagDirection in LazySets.jl does (cc @mforets ). Since LazySets.jl is an optional dependency used only in LinearOettliPrager, it would be good to have a more efficient version of list_orthants in IntervalLinearAlgebra.jl

Minimum working example

I'm not sure what would be a smart way to go, maybe define

struct Orthants
n::Int
end

and implement the iterators interface for that

Additional information